Generally, in wireless or radio communication networks, transmissions between radio base stations, RBSs, and user equipments, UEs, are affected by a plurality of circumstances and conditions. For example, the distance between an RBS and a UE may be short or long, which may affect the transmission such that higher transmission power is needed when the distance is relatively long as compared to when the distance is relatively short. Further, the presence of buildings, trees and other objects may cause reflections and other adverse affects to the signal being transferred from the RBS to the UE. Still further, the interference situation caused by other UEs and neighbouring RBSs may adversely affect the transmission.
There may further be other reasons for enhancing or improving the performance of the RBSs and UEs in a wireless or radio communication network. It is desirable to optimise the use of the available resources in the communication system.
One solution to enhance or improve the performance of the RBSs and UEs in a wireless or radio communication network is to employ pre-coding at the RBS before transmission of signals and/or data to one or more UEs. One example of pre-coding is Signal-to-Leakage- and-Noise-Ratio, SLNR. The SLNR pre-coding can offer relatively high performance by taking both multiuser interference and noise into account. On the other hand, the leakage-based optimization criterion adopted by SLNR pre-coding may yield a closed form solution. One shortcoming of the SLNR pre-coding is that it only tries to optimize the transmitter design without considering the impact of receivers.
In order to improve the SLNR pre-coding scheme, iterative SLNR pre-coding has been suggested. One example of an iterative SLNR pre-coding method is based on the maximum sum-rate criterion. The scheme jointly optimizes the precoder and the receiver in an iterative manner, and provides higher sum rate than that of conventional non-iterative SLNR pre-coding. However, the algorithm still has the following drawbacks.
One drawback is that the base station requires the full channel information of each user, which is not Frequency Division Duplex, FDD, friendly. Although channel reciprocity may be utilized in single-cell Time Division Duplex, TDD, transmission, a large amount of Channel State Information, CSI, will be exchanged between adjacent cells in multi-cell TDD systems, which inevitably increases processing latency at the base station, as well as the traffic load at the X2 interface. Therefore, for multi-cell or Coordinated Multipoint Transmission, CoMP, systems, the iterative algorithm is not a favourable choice.
Another drawback is that the RBS needs to know the UE's detection algorithm in advance. This assumption is indeed impractical since the detection algorithm adopted by each UE is proprietary.
Still a further drawback is that the iterative procedure may not converge, or converge very slowly, which leads to high computational complexity and processing delay.